353 research outputs found
Astrophysical signatures of leptonium
More than 10^43 positrons annihilate every second in the centre of our Galaxy
yet, despite four decades of observations, their origin is still unknown. Many
candidates have been proposed, such as supernovae and low mass X-ray binaries.
However, these models are difficult to reconcile with the distribution of
positrons, which are highly concentrated in the Galactic bulge, and therefore
require specific propagation of the positrons through the interstellar medium.
Alternative sources include dark matter decay, or the supermassive black hole,
both of which would have a naturally high bulge-to-disc ratio.
The chief difficulty in reconciling models with the observations is the
intrinsically poor angular resolution of gamma-ray observations, which cannot
resolve point sources. Essentially all of the positrons annihilate via the
formation of positronium. This gives rise to the possibility of observing
recombination lines of positronium emitted before the atom annihilates. These
emission lines would be in the UV and the NIR, giving an increase in angular
resolution of a factor of 10^4 compared to gamma ray observations, and allowing
the discrimination between point sources and truly diffuse emission.
Analogously to the formation of positronium, it is possible to form atoms of
true muonium and true tauonium. Since muons and tauons are intrinsically
unstable, the formation of such leptonium atoms will be localised to their
places of origin. Thus observations of true muonium or true tauonium can
provide another way to distinguish between truly diffuse sources such as dark
matter decay, and an unresolved distribution of point sources.Comment: Accepted for publication in EPJ-D, 9 pages, 4 figure
Smart city development as spatial manifestations of 21st century capitalism
Globally, smart cities attract billions of dollars in investment annually, with related market opportunities forecast to grow year-on-year. The enormous resources poured into their development consist of financial capital, but also natural, human and social resources converted into infrastructure and real estate. The latter act as physical capital storage and sites for the creation of digital products and services expected to generate the highest value added. Smart cities serve as temporary spatial fixes until new and better investments opportunities emerge. Drawing from a comprehensive range of publications on capitalism, this article analyzes smart city developments as typifier of 21st century capital accumulation where the financialization of various capitals is the overarching driver and ecological overshoot and socio-economic undershoot are the main negative consequences. It closely examines six spatial manifestations of the smart city â science parks and smart campuses; innovation districts; smart neighborhoods; city-wide and city-regional smart initiatives; urban platforms; and alternative smart city spaces â as receptacles for the conversion of various capitals. It also considers the influence of different national regimes and institutional contexts on smart city developments. This is used, in the final part, to open a discussion about opportunities to temper the excesses of 21st century capitalism.</p
An upper limit to the dry merger rate at <z> ~ 0.55
We measure the fraction of Luminous Red Galaxies (LRGs) in dynamically close
pairs (with projected separation less than 20 kpc and velocity
difference less than 500 km s) to estimate the dry merger rate for
galaxies with and
in the 2dF-SDSS LRG and QSO (2SLAQ) redshift survey. For galaxies with a
luminosity ratio of or greater we determine a upper limit to
the merger fraction of 1.0% and a merger rate of
Mpc Gyr (assuming that all pairs merge on the shortest possible
timescale set by dynamical friction). This is significantly smaller than
predicted by theoretical models and suggests that major dry mergers do not
contribute to the formation of the red sequence at .Comment: 8 pages emulateapj style, 3 figures, accepted by AJ (March 2010
Eco-neighborhoods and the question of locational advantage: a socio-spatial analysis of French âĂcoQuartiersâ
In response to the need for ecological transition, a multitude of eco-city and eco-neighborhood initiatives have been instigated around the world. A major challenge has been the charge, captured by terms such as âeco enclavesâ and âenvironmental gentrificationâ, that these initiatives poorly attend to questions of social diversity and spatial equity. In France, too, where since 2008 a major national ĂcoQuartier initiative has been underway with close to 500 projects launched, some have warned against creating âĂŠcoquartiers boboâ â urban development catering for a mainly âbourgeois-bohemianâ clientele. Consequently, this article investigates whether there may be selectivity at work in the placement of ĂcoQuartiers that favours advantageous locations. To this end, a detailed socio-spatial analysis was carried out with a sample of 214 implemented ĂcoQuartiers. Using exploratory factor analysis (EFA), eight factors were extracted from a comprehensive set of 53 socio-economic and geospatial variables. These were used to compare the sampled ĂcoQuartiers with the overall territory (mainland France and Corsica) as well as with a parallel national urban policy initiative, the âQuartiers Prioritaires de la Villeâ (âurban priority neighborhoodsâ) which expressly focuses on areas of social disadvantage. As a result, this study reveals several dimensions of locational selectivity, which are discussed in terms of their policy and practice implications as well as their significance for conceptualizing eco-neighborhoods as socio-spatially inclusive places
Smart cities as spatial manifestations of 21st century capitalism
Globally, smart cities attract billions of dollars in investment annually, with related market opportunities forecast to grow year-on-year. The enormous resources poured into their development consist of financial capital, but also natural, human and social resources converted into infrastructure and real estate. The latter act as physical capital storage and sites for the creation of digital products and services expected to generate the highest value added. Smart cities serve as temporary spatial fixes until new and better investments opportunities emerge. Drawing from a comprehensive range of publications on capitalism, this article analyzes smart city developments as typifier of 21st century capital accumulation where the financialization of various capitals is the overarching driver and ecological overshoot and socio-economic undershoot are the main negative consequences. It closely examines six spatial manifestations of the smart city â science parks and smart campuses; innovation districts; smart neighborhoods; city-wide and city-regional smart initiatives; urban platforms; and alternative smart city spaces â as receptacles for the conversion of various capitals. It also considers the influence of different national regimes and institutional contexts on smart city developments. This is used, in the final part, to open a discussion about opportunities to temper the excesses of 21st century capitalism
Dynamic optimization of the transmission efficiency between the solid state microwave sources and the microwave applicator
[EN] Microwaves are a fast way to dry moist goods through volumetric heating. During the drying process, materials change their electrical properties. As a result, the impedances at the feed port of the applicator will change and the microwave source is not matched anymore. The amount of reflected power increases and the process efficiency reduces. New semiconductor high power sources can perform a dynamic impedance matching. A lab scaled functional model with two sources was designed and realized. For measuring the scattering parameters during the process run, an embedded two-port vector network analyzer was added. Measurement results confirm the feasibility of the concept.Zuber, S.; Joss, M.; Tresch, S.; Kleingries, M. (2018). Dynamic optimization of the transmission efficiency between the solid state microwave sources and the microwave applicator. En IDS 2018. 21st International Drying Symposium Proceedings. Editorial Universitat Politècnica de València. 291-298. https://doi.org/10.4995/IDS2018.2018.7412OCS29129
Smart Cities: Towards a New Citizenship Regime? A Discourse Analysis of the British Smart City Standard
Growing practice interest in smart cities has led to calls for a less technology-oriented and more citizen-centric approach. In response, this articles investigates the citizenship mode promulgated by the smart city standard of the British Standards Institution. The analysis uses the concept of citizenship regime and a mixture of quantitative and qualitative methods to discern key discursive frames defining the smart city and the particular citizenship dimensions brought into play. The results confirm an explicit citizenship rationale guiding the smart city (standard), although this displays some substantive shortcomings and contradictions. The article concludes with recommendations for both further theory and practice development
Seeking celestial Positronium with an OH-suppressed diffraction-limited spectrograph
Celestially, Positronium (Ps), has only been observed through gamma-ray
emission produced by its annihilation. However, in its triplet state, a Ps atom
has a mean lifetime long enough for electronic transitions to occur between
quantum states. This produces a recombination spectrum observable in principle
at near IR wavelengths, where angular resolution greatly exceeding that of the
gamma-ray observations is possible. However, the background in the NIR is
dominated by extremely bright atmospheric hydroxyl (OH) emission lines. In this
paper we present the design of a diffraction-limited spectroscopic system using
novel photonic components - a photonic lantern, OH Fiber Bragg Grating filters,
and a photonic TIGER 2-dimensional pseudo-slit - to observe the Ps Balmer alpha
line at 1.3122 microns for the first time.Comment: 6 pages, 9 Figures, 2 Tables. Accepted to Applied Optics feature
issue on Astrophotonic
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